Adaptive robust control of fully-constrained cable driven parallel robots

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.     

果林机器人行走驱动闭环控制分析

该研究旨在选取控制机器人运动的合理方式。以履带式果林机器人为背景,分析了果林机器人运动双电机控制系统。基于步进直流电机转速增量式PID闭环控制算法,计算了PID控制器比例系数、积分系数和微分系数。仿真和试验表明：当机器人左、右电机以3 000 r/min的速度在地面上直线运行时,采用转速增量式PID控制比开环控制电机响应速度快,稳定性能好。结果提示,转速增量式PID控制方式是有效合理的。     

A saturation-type robust controller for modular manipulators arms

This paper presents a new robust controller for modular and reconfigurable manipulators that require frequent conversion from one setup to another in industrial applications. The proposed robust controller can be integrated with a typical industrial proportional-integral-derivative (PID) controller and only requires the boundaries of the uncertainties of the dynamic parameters of the robotic arm. This makes the proposed controller easy to configure and implement for various setups realized from a reconfigurable robot and guarantees uniform ultimate boundedness of all tracking errors.A numerical analysis is presented to validate the effectiveness of the proposed controller. The performance of the proposed robust controller is compared to that of an independent joint PID controller for two different 3-DOF robotic configurations.     

Intelligent optimal control of single-link flexible robot arm

This paper addresses the design and properties of an intelligent optimal control for a nonlinear flexible robot arm that is driven by a permanent-magnet synchronous servo motor. First, the dynamic model of a flexible robot arm system with a tip mass is introduced. When the tip mass of the flexible robot arm is a rigid body, not only bending vibration but also torsional vibration are occurred. In this paper, the vibration states of the nonlinear system are assumed to he unmeasurable, i.e., only the actuator position can be acquired to feed into a suitable control system for stabilizing the vibration states indirectly. Then, an intelligent optimal control system is proposed to control the motor-mechanism coupling system for periodic motion. In the intelligent optimal control system a fuzzy neural network controller is used to learn a nonlinear function in the optimal control law, and a robust controller is designed to compensate the approximation error. Moreover, a simple adaptive algorithm is proposed to adjust the uncertain bound in the robust controller avoiding the chattering phenomena. The control laws of the intelligent optimal control system are derived in the sense of optimal control technique and Lyapunov stability analysis, so that system-tracking stability can be guaranteed in the closed-loop system. In addition, numerical simulation and experimental results are given to verify the effectiveness of the proposed control scheme.     

Mechatronic design of a class of planar cable-driven parallel robots

In this paper, a novel class of planar cable-driven parallel robots is discussed. The design allows an arbitrary rotation of the end effector by wrapping the cables around a cylindrical fixture on the end-effector platform. In contrast to the state of the art, this results in a simple and robust design without additional moving parts attached to the end effector. The inverse kinematics and dynamical equations of motion for this class of robot are derived and analyzed. Furthermore, the motor redundancy is resolved by enforcing a required tension in the cables. Classical manipulability measures known from the literature are found to be inappropriate for the analysis of cable-driven robots. In order to capture the minimum tension in the cables and the directional dependence of the achievable forces, which are the determining factors for the workspace, a new force manipulability measure is employed. The mechanical design of an experimental setup is presented and the main design choices are elaborated. The experimental results demonstrate the feasibility of the proposed approach and validate the theoretical investigations.     

Genetic algorithm tuning of Lyapunov-based controllers: anapplication to a single-link flexible robot system

In this paper, a systematic controller design approach is proposed to guarantee both closed-loop stability and desired performance of the overall system by effectively combining genetic algorithms (GAs) with Lyapunov's direct-controller design method. The effectiveness of the approach is shown by using a simple and efficient decimal GA optimization procedure to tune and optimize the performance of a Lyapunov-based robust controller for a single-link flexible robot. The feedback gains of the controller are tuned by the GA optimization process to achieve good results for tip motion control of the single-link flexible robot based on some suitable fitness functions. The paper includes results of simulation experiments demonstrating the effectiveness of the proposed genetic algorithm approach     

Admittance controller complemented with real-time singularity avoidance for rehabilitation parallel robots

Rehabilitation tasks demand robust and accurate trajectory-tracking performance, mainly achieved with parallel robots. In this field, limiting the value of the force exerted on the patient is crucial, especially when an injured limb is involved. In human–robot interaction studies, the admittance controller modifies the location of the robot according to the user efforts driving the end-effector to an arbitrary location within the workspace. However, a parallel robot has singularities within the workspace, making implementing a conventional admittance controller unsafe. Thus, this study proposes an admittance controller that overcomes the limitations of singular configurations by using a real-time singularity avoidance algorithm. The singularity avoidance algorithm modifies the original trajectory based on the actual location of the parallel robot. The complemented admittance controller is applied to a 4 degrees of freedom parallel robot for knee rehabilitation. In this case, the actual location is measured by a 3D tracking system because the location calculated by the forward kinematics is inaccurate in the vicinity of a singularity. The experimental results verify the effectiveness of the proposed admittance controller for safe knee rehabilitation exercises.     

Robotic system for underwater inspection of bridge piers

The research objective is to develop an automated robotic system that will enable safe and cost-effective underwater inspection of bridge substructures. The system concept being developed is a semiautonomous robotic system that can carry a sensor platform underwater to detect scour, deterioration, or damage to support columns. It provides positional data and sensor information (video images) to the system operator; these can be verbally annotated while being recorded. The operator initiates basic commands and transmits them to the underwater apparatus. On-board microprocessor-based controllers automatically accomplish the detailed control. The primary underwater apparatus has a team of two identical mobile robots designed to travel along opposite surfaces of the pier while connected to each another by a cable and winch system. Each robot has rubber tracks or wheels with cleats and is driven by internal motors. Tensioning the cables that connect the two robots provides traction. The robots can move both vertically and horizontally. While each robot operates its own drive motors and cable winches, coordination of movement and cable tensioning occurs automatically through feedback between the robots and the control console. Multiple robots, evenly spaced around a support column, may inspect larger structures     

A hybrid fuzzy logic and neural network algorithm for robot motioncontrol

Robotic manipulators are multivariable nonlinear coupling dynamic systems. Industrial robots were controlled by using a traditional controller, the control performance of which may change with respect to operating conditions. Since the robotic manipulators have complicated nonlinear mathematical models, control systems based on the system model are difficult to design. In this paper, a model-free hybrid fuzzy logic and neural network algorithm was proposed to control this multi-input/multi-output (MIMO) robotic system. First, a fuzzy logic controller was designed to control individual joints of this 4-degree-of-freedom (DOF) robot. Secondly, a coupling neural network controller was introduced to take care of the coupling effect among joints and refine the control performance of this robotic system. The experimental results showed that the application of this control strategy effectively improved the trajectory tracking precision     

Dynamic trajectory planning study of planar two-dof redundantly actuated cable-suspended parallel robots

This paper analyzes a set of dynamic trajectories for planar two-dof redundantly actuated cable-suspended parallel mechanisms. In recent literature, the global dynamic trajectory planning problem of cable-suspended mechanisms was addressed and some of the characteristic properties of such robots were revealed. In this paper, actuation redundancy is introduced and the dynamic trajectory planning is addressed using a series of periodic trajectories (i.e. straight line and circular periodic trajectories) and the application of the antipodal theorem. The experimental results obtained show that introducing actuation redundancy increases the dynamic capabilities of the robots. Also, cable tensions acquired via tension sensors confirm that cables always remain taut during all experimental verifications at feasible frequencies and that they are consistent with the tension variations predicted by theory. Furthermore, special frequencies are specified that are similar to those encountered with non-redundant mechanisms. Additionally, an alternative architecture is proposed to deal with cable interferences and it is shown that the novel architecture leads to improved dynamic capabilities when compared to the original architecture.     

Chaos synchronization using higher-order adaptive PID controller

This paper is devoted to designing higher-order adaptive PID controllers as a new generation of PID controllers for chaos synchronization, in which second order integration and second-order derivative terms to the PID controller (PII²DD²) are employed. The five PII²DD² control gains are updated online with a stable adaptation law driven by Lyapunov’s stability theory. This is the unique advantage of the proposed approach. Furthermore, it is equipped with a novel robust control term to improve controller robustness against system uncertainties and unknown disturbances. An important feature of the proposed approach is that it is a model-free controller. In addition, to determine the control design parameters and avoid trial and error, the Teaching–learning-based optimization algorithm (TLBO) is employed to regulate these parameters and enhance the performance of the proposed controller. Based on the Lyapunov stability theory, it is proven that the proposed control scheme can guarantee the synchronization and the stability of closed-loop control system. The case study is the Duffing–Holmes oscillator. Comparative simulation results are presented which confirm the superiority of the proposed approach.     

Combined kinematic and dynamic control of vehicle-manipulator systems

A vehicle-manipulator system (VMS) is a class of mobile robots characterised by their ability to carry or be a robotic arm and therefore also manipulate objects. The VMS class includes vehicles with a robotic manipulator, free-floating space robots, aerial manipulators and underwater vehicle-manipulator systems (UVMSs). All of these systems need a kinematic controller to solve the kinematic redundancy of the VMS and a dynamic controller to follow the reference given by the kinematic controller. In this paper, we propose a combined kinematic and dynamic control approach for VMSs. The approach uses the singularity-robust multiple task-priority (SRMTP) framework to generate a velocity reference combined with a dynamic velocity controller based on a robust sliding mode controller (SMC). Any SMC can be used as long as it can make the velocity vector converge to the velocity reference vector in finite time. This novel approach allows us to analyse the stability properties of the kinematic and dynamic subsystems together in the presence of model uncertainty. We show that the multiple set-point regulation tasks will converge asymptotically to zero without the strict requirement that the velocities are perfectly controlled. This novel approach thus avoids the assumption of perfect dynamic control that is common in kinematic stability analyses for robot manipulators. We present two examples of SMCs that can make the velocity vector converge to the velocity reference vector in finite time. We also demonstrate the applicability of the proposed approach through a simulation study of an articulated intervention-AUV (AIAUV), which is a type of UVMS, by conducting three simultaneous tasks. The results show that both SMC algorithms can make all the regulation tasks converge to their respective set-points. In the simulation study, we also include the results from two standard control methods, a proportional-integral-derivative (PID) controller and a feedback linearisation controller, and we use two different AIAUVs to illustrate the advantages and robustness achieved from using SMC.     

Robust design of independent joint controllers with experimentationon a high-speed parallel robot

A linear independent joint control scheme is proposed. The design is made robust by closing another feedback loop that uses acceleration information besides the typical position and velocity loops. Reconstruction of acceleration measurements is performed via a suitable state-variable filter. Linear feedforward compensation is used to improve tracking performance of the closed-loop scheme. The control algorithm is tested first in a discrete-time simulation on a single-joint drive system with imposed disturbance torques. Then, real-time implementation on a high-speed parallel robot is presented. The experimental results demonstrate the effectiveness of the proposed technique     

Computationally Efficient Predictive Robot Control

Conventional linear controllers (PID) are not really suitable for the control of robot manipulators due to the highly nonlinear behavior of the latter. Over the last decades, several control methods have been proposed to circumvent this limitation. This paper presents an approach to the control of manipulators using a computationally-efficient-model-based predictive control scheme. First, a general predictive control law is derived for position tracking and velocity control, taking into account the dynamic model of the robot, the prediction and control horizons, and also the constraints. However, the main contribution of this paper is the derivation of an analytical expression for the optimal control to be applied that does not involve a numerical procedure, as opposed to most predictive control schemes. In the last part of the paper, the effectiveness of the approach for the control of a nonlinear plant is illustrated using a direct-drive pendulum, and then, the approach is validated and compared to a PID controller using an experimental implementation on a 6-DOF cable-driven parallel manipulator.     

Hybrid fault adaptive control of a wheeled mobile robot

A fault adaptive control methodology for mobile robots is presented. The robot is modeled as a continuous system with a supervisory controller. The physical processes of the robot are modeled using bond graphs, and this forms the basis of a combined qualitative reasoning and quantitative model-based estimation scheme for online fault detection and isolation during robot operation. A hierarchical-control accommodation framework is developed for the supervisory controller that determines a suitable control strategy to accommodate the isolated fault. It is shown that for small degradations in actuation effort, a robust controller achieves fault accommodation without significant loss of performance. However, for larger faults, the supervisor needs to switch among several controllers to maintain acceptable performance. The switching stability among a set of trajectory tracking controllers is presented. Simulation results verify the proposed fault adaptive control technique for a mobile robot.     

减重支持系统的实现

介绍了康复机器人减重支持系统的构成。利用直线执行器作为支持系统的主要部件,采用H桥驱动直线执行器。利用双闭环反馈控制作为该系统的控制器,其中电流控制器作为内环控制器,速度反馈控制器作为外环控制器,并均采用PID控制器来实现,PID参数采用遗传算法进行整定。同时,利用延迟采样的策略保证了电流控制器参数的正确性。从实际效果上看,双闭环反馈控制基本使减重支持系统达到了恒力输出的要求。     

A new set-point controller with bounded torques for robotmanipulators

In this paper, we propose a simple controller for set-point control of robot manipulators. The structure of this controller is composed by a saturated proportional-saturated derivative feedback plus gravity compensation. Such a control scheme has two practical features. First, for all desired joint positions, this controller delivers torques inside prescribed limits according to the actuator capability and second, the steady-state position errors owing to static friction can be arbitrarily reduced. In the case of absence of friction, we show global asymptotic stability of the closed-loop system. The performance of the proposed controller is illustrated via experiments on a two-degrees-of-freedom (2-DOF) direct-drive robot system     

An interaction controller formulation to systematically avoid force overshoots through impedance shaping method with compliant robot base

Nowadays, light-weight manipulators are widely adopted in many applications requiring manipulation/interaction with compliant/fragile objects. Reduced inertia and controlled compliance, indeed, make such manipulators particularly attractive when compliant mountings (or mobile platforms) are adopted and contact force overshoot may compromise the application. The here presented work proposes the design of a force-tracking controller for interaction tasks allowing to systematically avoid any force overshoot for lightweight robots mounted on compliant bases. The developed algorithm allows to compensate for the compliant robot base dynamics that affects the interaction. The control gains are calculated to track a target force reference through the estimation of the robot base state and the interacting environment stiffness. Closed-loop stability and control gains calculation are described. The control law has been validated in a probing task involving a compliant robot base and a compliant environment to show the obtained performance.     

Servo System Using Optical Serial Transmission in Control Loop for Industrial Robots

A new servo system suitable for robot control is proposed. An optical serial transmission is applied in its servo-control loops to reduce the number of signal cables and the cable length between the robot mechanism and the controlling equipment, as well as to increase flexibility for expanding control functions.     

Analysis of stiffness controllability of a redundant cable-driven parallel robot based on its configuration

To examine the influence of the configuration of a cable-driven parallel robot (CDPR) on its stiffness and stiffness controllability, a concept for a cable tension constraint workspace (CTCW) of CDPRs is introduced. Using a static force analysis, a static CDPR model was established and its stiffness model and a method for optimizing the cable tension were reviewed. To analyze and appraise the CDPR global and local stiffness controllability, a new concept of stiffness controllability degree is proposed and defined. In addition, a calculation method is proposed that uses the cable tension feasible region to effectively obtain the CTCW of the CDPRs according to the cable tension constraint condition. The driving cable layouts of the various CDPR configurations were optimized to maximize the CTCW volume as a performance index. In addition, the stiffness and stiffness controllability of each configuration CDPR were analyzed. The results of the theoretical and experimental analyses validated the efficacy of the presented method and serve as reference for the use of robots in practical applications or for design optimization.